Various power applications require reliable battery operation and accurate monitoring during operation. For example, an Uninterruptible Power Supply (UPS) provides backup power to a load, such as a computing or telecommunications device, when a primary power source has stopped providing power (e.g., due to failure). Accurate monitoring of the UPS battery charge state facilitates a user to suitably save information and shutdown the device before the UPS reaches end-of-discharge. As another example, a vehicle battery provides power to propel an electric vehicle. Accurate monitoring of the vehicle battery charge state provides an indication to an operator of the electric vehicle of how long they can drive the electric vehicle before stopping to charge the vehicle battery.
In one approach, a battery system provides battery status indicators that are based on state of charge (SOC) or voltage. In another approach, a battery system attempts to track power delivery by correlating capacity and initial resistance of the battery through off-line testing prior to use. In yet another approach, an indication of battery status is derived from counting discharge cycles or charge throughput and reporting on a relative health degradation based upon a-priori testing of a battery on a standardized load test.